Is cold fusion truly impossible, or is it just that no respectable scientist can risk their reputation working on it? by Huw Price

A few years ago, a physicist friend of mine made a joke on Facebook about the laws of physics being broken in Italy. He had two pieces of news in mind. One was a claim by a team at the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) in Gran Sasso, who said they’d discovered superluminal neutrinos. The other concerned Andrea Rossi, an engineer from Bologna, who claimed to have a cold fusion reactor producing commercially useful amounts of heat.

Why were these claims so improbable? The neutrinos challenged a fundamental principle of Albert Einstein’s theory of special relativity, which says that nothing can travel faster than light. Meanwhile cold fusion (or LENR, for ‘low-energy nuclear reaction’) is the controversial idea that nuclear reactions similar to those in the Sun could, under certain conditions, also occur close to room temperature.

The latter was popularised in 1989 by Martin Fleischmann and Stanley Pons, who claimed to have found evidence that such processes could take place in palladium loaded with deuterium (an isotope of hydrogen). A few other physicists, including the late Sergio Focardi at Bologna, claimed similar effects with nickel and ordinary hydrogen. But most were highly skeptical, and the field subsequently gained, as Wikipedia puts it, ‘a reputation as pathological science’.

It turned out that my physicist friend and I disagreed about which of these unlikely claims was most credible. He thought it was the neutrinos, because the work had been done by respectable scientists rather than a lone engineer with a somewhat chequered past. I favoured Rossi, on grounds of the physics. Superluminal neutrinos would overturn a fundamental tenet of relativity, but all Rossi needed was a previously unnoticed channel to a reservoir of energy whose existence is not in doubt. We know that huge amounts of energy are locked up in metastable nuclear configurations, trapped like water behind a dam. There’s no known way to get useful access to it at low temperatures. But – so far as I knew – there was no ‘watertight’ argument that such methods were impossible....